Operation of radio broadcast stations



March 2, 1937. p SCHARRER 2,072,279

OPERATION OF RADIO BROADCAST STATIONS Original Filed Dec. 15, 1931 INVENTOR PAUL SCH RER BY MVf/C ATTORNEY Patented Mar. 2, 1937 UNITED STATES PATENT OFFICE OPERATION OF RADIO BROADCAST STATIONS Application December 15, 1931, Serial No. 581,167. Renewed June 15, 1935. In Germany December 22, 1930 5 Claims.

It has been suggested in the prior art to connect or disconnect broadcast receiving stations automatically at certain times. Arrangements of this kind known in the earlier art are often operated by a time clock with switching means set to definite operating times. However, the items on the program of a broadcast transmitting station do not always start at an exactly predetermined instant, and for this reason it would be necessary to insure certain time tolerance limits between the various program items which in turn means more or less long intermissions between them with the result that the operating time of the receiver is unnecessarily extended.

The object of this invention is to provide a method and means to operate broadcast stations which makes it possible to connect the loudspeaker in a receiver set at the instant when the next item commences without any prior adjustment of the switching time.

According to the invention, a brief time previous to the beginning of each program item to be transmitted, a frequency is impressed upon the transmitted carrier wave whereby at the receiving stations a contactor or relay is influenced whereby the loudspeaker in the receiving set is switched in.

Most suitable is a resonance or tuned relay designed to respond to a definite frequency of certain minimum duration. This relay is connected in parallel to the loudspeaker of the receiver set in such a manner that by the aid of a change-over switch either the relay or instead of that the loudspeaker is adapted to be cut in the receiver apparatus. The relay so acts upon the said change-over switch that upon response to the superposed switching frequency it becomes disconnected while the loudspeaker is cut in circuit. The superposed frequency is most suitably so chosen that it lies below the audible acoustic frequency or near the same.

The drawing shows a switch arrangement according to the invention intended for receiving sets.

Referring to the drawing, l and 2 denote the terminals which are associated with the output points of a receiver R. Connected with the terminals 3 and 4 is the loudspeaker. The resonant relay comprises an electromagnet 5 which is disposed at the pole of a permanent magnet 6. At the other pole of the said permanent magnet 6 is attached a vibratory or elastic tongue or ditton or blade 8. The latter carries a keeper which is located inside the air-gap of the electromagnet 5. The said elastic blade and the keeper thereof are so dimensioned that the period of oscillation corresponds to the acoustic frequency to which the relay is to respond.

l8 denotes a switch lever which is operable by a handle iii. The said lever I8 is connected with the terminal i. The lever l8 acts upon a contact device I I and i2, one contact piece thereof is united as shown with the terminal 3 and the other one with the winding of the electromagnet 5. The other end of the magnet coil 5 is united with terminals 2 and 4. Acting upon the switch lever I8 is an elastic latch or pawl l3 whose other end is placed opposite an extension of the elastic blade or ditton 8.

If the receiving set coupled with the above switching wave sent out from the broadcast station, the oscillatory system of the resonant relay is caused to vibrate. In case of sufficiently long duration of the said switching wave, the amplitude of the oscillating system becomes adequately large in order to move the pawl 13 and release the switch lever i8. The lever thus disconnects the relay and connects in its stead the loudspeaker.

The form of construction and the arrangement of the relay responsive to the switching frequency may be chosen ad libitum. Instead of the polarized magnet system it would also be possible to use an ordinary electromagnet if the time of vibration of the oscillatory system is given a correspondingly different natural frequency.

The method of this invention offers this further advantage that the switch device associated with the receiver set is comparatively simple and that no clockwork mechanism is required. The invention is furthermore useful also for other switching actions to be effected in receiving sets from the broadcast station. It may be of advantage in this connection to use several switching frequencies independent of each other. In this case either several differently tuned resonant relays are mounted in the receiving set or else a resonant relay is so arranged that its oscillatory system is adjustable to two or more frequencies.

It is also feasible to utilize the intermission signal customary in broadcast transmissions simultaneously for the release of the switch relay disposed in the receiver set. For instance, if the said intermission signal consists of a regular sequence of cadences the relay may be so designed that by the action of the same it is caused to respond in resonance with the result that thereby the loudspeaker is connected in circuit.

I claim:

1. In a radio communication system wherein just prior to the beginning of the transmission of each particular program from a transmitter a characteristic signal is transmitted, a receiver including a translating device, a relay, means for connecting said relay across the output of the receiver comprising a settable double throw switch adapted to be manually set to render the translating device inoperative and the relay in condition to be operated by the incoming characteristic signal, and means responsive to the receipt of the characteristic signal for tripping said switch thereby disconnecting said relay from said output and rendering the translating device operative.

2. In a communication system wherein a characteristic signal is transmitted from the respective transmitter stations just prior to the start of the transmission of each particular program period, a receiver provided with a signal translating device, an operable relay associated with the receiver output and including a selector switch device adapted to be set with respect to the translating device and the relay so as to render the translating device unresponsive to signals received by the receiver and the relay in condition to be operated by the desired incoming characteristic signal, and means responsive to the receipt of the desired characteristic signal to indicate the beginning of a particular program period from a particular transmitting station for operating the selector switch to thereby render the relay inoperative and the translating device responsive to the signals received by the receiver.

3. In radio communication systems, wherein just prior to the beginning of a program transmission from a transmitter a characteristic signal of a frequency which is outside the audible range is transmitted, a receiver including a translating device, a relay, means for connecting said relay across an output point of the receiver comprising a settable double throw switch adapted to be manually set to prevent transmission of energy to the translating device and to condition the relay so as to be operated by the incoming characteristic signal, and means responsive to the receipt of the characteristic signal for tripping said switch and thereby disconnecting said relay from said output point to permit transmission of energy to the translating device.

4. In radio communication systems wherein just prior to the beginning of a program transmission from a transmitter a sub-audible frequency characteristic signal is transmitted by modulating the transmitter carrier wave therewith, a receiver including a translating device, a relay, means for connecting the relay across the output of the receiver comprising a settable double throw switch adapted to be manually set to prevent the transmission of energyto the translating device and to condition the relay so as to be operated by the incoming characteristic signal, and means responsive to the receipt of the characteristic signal for tripping said switch and thereby disconnect the relay from said output to permit transmission of energy to the translating device.

5. In a communication system wherein there is initiated the transmission of a characteristic signal of a frequency below the audible range 1 just prior to the start of each program transmission period from any transmission point, a receiver providedwith asignal translating device, an operable relay associated with the receiver and including a selector switch device adapted to be 

